1. Field of the Invention
The present invention relates to an antenna apparatus and an antenna system.
2. Description of Related Art
In earlier development, for example, a viewer has adjusted the direction and the like of an antenna, referring to an image displayed on a display unit so that the antenna may face the optimum reception direction at the time of the reception of a television broadcast signal (hereinafter referred to as a “TV broadcast signal”) with an antenna system. However, the adjustment method has a problem of being very troublesome. Consequently, there have been proposed, for example, the antenna system equipped with an indicator that can display the reception situation of a TV broadcast signal so as to enable a viewer to manually adjust the direction and the like of the antenna, with the viewer referring to a reception situation displayed on the indicator (see, for example, Japanese Patent Application Publication Laid-open No. 2001-94899), the antenna system capable of automatically adjusting the direction and the like of the antenna when a viewer requests the adjustment (see, for example, Japanese Patent Application Publication Laid-open No. 2001-86019), and the like.
Furthermore, there has been also proposed the antenna system equipped with an antenna apparatus including an antenna capable of automatically switching the directivity thereof whenever a viewer specifies a desired channel (called as a “smart antenna” as a popular name) and a television receiver. To put it concretely, for example, the antenna apparatus is controlled by the television receiver based on a predetermined standard such as EIA/CEA-909 to switch the directivity and the like of the smart antenna.
Now, TV broadcast signals can be classified to the signals in a first frequency band (for example, the VHF band) (hereinafter referred to as “VHF signals”) and the signals in a second frequency band (for example, the UHF band) (hereinafter referred to as “UHF signals”) based on their frequency bands, and the configuration of an antenna for VHF signal reception greatly differs from that of an antenna for UHF signal reception. Consequently, for example, if it is tried to modify the configuration of the aforesaid smart antenna so as to be able to receive both the VHF signals and the UHF signals, then the problem of the enlargement in size of the smart antenna is caused. On the other hand, the reason why the smart antenna has many directivity directions is to deal with the case where transmission towers for transmitting TV broadcast signals are built to be dotted about, and the like. However, the broadcasting in the VHF band has been reduced with the recent transition from the analog broadcasting to the digital broadcasting, and the possibility that the VHF signals are transmitted from more directions is little in the future. That is, the need to switch the directivity of an antenna at the time of receiving a VHF signal is little, and it is sufficient for an antenna capable of receiving both of the VHF signals and the UHF signals to have the ability of switching the directivity thereof at least at the time of receiving a UHF signal.